Method and apparatus for degrading antimisting fuel

ABSTRACT

A centrifugal pump is provided for degrading antimisting fuel. The centrifugal pump has a rotary impeller closely surrounded by a vaned diffuser for receiving fuel therefrom. The diffuser includes a plurality of recirculation channels disposed along its inner circumferential surface for directing some of the fuel which passes from the impeller to the diffuser back to the impeller for enhancing the degradation of the fuel. Other embodiments are disclosed.

The invention herein described was made in the course of, or under, acontract with the Department of Transportation.

This is a continuation of application Ser. No. 625,269, filed June 27,1984, now abandoned, which is a division of application Ser. No.370,238, filed Apr. 21, 1982, now U.S. Pat. No. 4,474,530, issued Oct.2, 1984.

BACKGROUND OF THE INVENTION

The present invention relates to method and apparatus for degradingantimisting fuel, and more particularly, to such method and apparatusemploying a centrifugal pump.

Interest in the use of engine fuels in gas turbine engine applications,e.g., aircraft engines, as a means to control or reduce crash andpostcrash fire fatalities has resulted in development of antimistingfuel. The antimisting fuel typically comprises kerosene containing anadditive which alters the fuel to provide long-chain molecule polymers.These long-chain molecule polymers provide the fuel with the ability toresist the tendency to mist and ignite in the event of crash orpostcrash tank or fuel line rupture.

However, in order for such antimisting fuel to be properly ignited andburned in the engine combustor, it is necessary to degrade the fuel backto its original kerosene molecule structure. In addition, due to thenon-Newtonian and highly viscous characteristic of the antimisting fuel,it is also necessary to degrade the antimisting fuel in order to providesatisfactory heat transfer in the engine heat exchangers generallyassociated with gas turbine engine applications. It is also desirable todegrade the antimisting fuel to ensure predictable leakage in fuelmetering components and to avoid blockage of fuel filters.

Centrifugal pumps are well known in gas turbine engine technology. Forexample, an exemplary centrifugal pump is described in U.S. Pat. No.3,784,318, entitled "Variable Diffuser Centrifugal Pump," assigned tothe assignee of the present application, and hereby incorporated intoreference in the present application. Such centrifugal pumps typicallyhave a rotary impeller closely surrounded by a collector, e.g., a vaneddiffuser, with the impeller having an input for receiving fuel and anoutput for directing the fuel therefrom into an input of the surroundingcollector. Such centrifugal pumps are capable of pumping fuel at thepressure and flow levels, e.g., typically about 1000 psi (pounds persquare inch) and 16000 pph (pounds per hour), respectively, required formany gas turbine engine applications. In addition, such pumps mustoperate at required speed ranges in the order of about 25000 rpm.

In order to employ such a centrifugal pump with antimisting fuel,however, additional means must be provided for degrading the antimistingfuel as conventional centrifugal pumps provide either no degradingcapability or unacceptably insufficient degrading capability. Thus, ithas been proposed to add degrading structures e.g., throttling devicesor cavitating devices, in serial flow relation with the centrifugalpump, thereby providing the required degrading function. However, suchadditional degrading structures are undesirable due to the additionalfuel system complexity and additional failure potentials introducedtherewith. In addition, such additional degrading structures typicallyrequire a significant increase in engine power extracted and often causethe fuel temperature to rise unacceptably, e.g., to levels over 300° F.at the fuel nozzles.

Thus, it would therefore be desirable to provide a conventionalcentrifugal fuel pump having the capability to degrade antimisting fuel.More particularly, it would be desirable to provide such a pump havingthe capability to pump fuel at the pressure and flow levels required ingas turbine engine applications, such as aircraft applications, as wellas the capability to simultaneously degrade antimisting fuel.

Accordingly, it is a general object of the present invention to provideimproved method and apparatus for degrading antimisting fuel.

It is another object of the present invention to provide such method andapparatus which includes an improved centrifugal pump.

It is another object of the present invention to provide such acentrifugal pump which operates as a relatively high flow rangecentrifugal pump while degrading antimisting fuel.

It is another object of the present invention to provide such acentrifugal pump having recirculation means for enhancing thedegradation of antimisting fuel.

It is another object of the present invention to provide such acentrifugal pump which can be provided through simple modification to aconventional centrifugal pump.

SUMMARY OF THE INVENTION

In carrying out one form of my invention, I provide a method fordegrading antimisting fuel. The method includes the step of providing acentrifugal pump of the type having a rotary impeller closely surroundedby a vaned collector. The impeller includes a substantially centrallylocated input for receiving fuel and an output for directing the fueloutwardly therefrom into an input of the vaned collector. The methodincludes the step of introducing antimisting fuel into the input of therotary impeller. The method includes the step of rotating the rotaryimpeller to create molecular forces in a degradation region disposedsubstantially between the rotary impeller and the vaned collectorwherein the forces are sufficient to degrade the antimisting fuel as thefuel passes through the degradation region into the input of the vanedcollector.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention, reference may be had to thefollowing description, taken in conjunction with the accompany drawings,wherein:

FIG. 1 is a sectional view showing one form of Prior Art centrifugalpump to which applicant's invention relates.

FIG. 2 is a sectional view of a centrifugal pump of the type of FIG. 1.

FIG. 3 is a simplified diagrammatic representation, taken similarly toFIG. 2, showing the manner in which antimisting fuel is degraded in oneform of the centrifugal pump of the present invention.

FIG. 4 is a curve showing the degradation characteristics of the PriorArt configuration pump of FIG. 1.

FIG. 5 is a curve showing the degradation chacteristics of the form ofcentrifugal pump shown partially in FIG. 2.

FIG. 6 is a sectional view, taken similarly to FIG. 1, showing a portionof another form of centrifugal pump of the present invention in which anaxial recirculation channel is provided.

DETAILED DESCRIPTION OF THE INVENTION

Referring initially to FIG. 1, an exemplary Prior Art centrifugal pumpto which applicant's invention relates is generally designated 10. Thepump 10 includes a centrally located axial inlet 12 for receiving aninput flow of the fuel to be pumped. A rotating impeller wheel 14 isprovided and includes a plurality of impeller blades 16 definingimpeller blade passageways 19 therebetween. The blades 16 are disposedinternally within axially opposing shroud portions 17. A casing 18 isprovided and defines a radial outlet 20, which surrounds the tips 16A ofthe impeller blades 16. A stationary vaned collector 22, e.g., diffuser,surrounds the radial outlet 20 and includes a plurality of stationarydiffuser vanes 24. Each pair of the diffuser vanes 24 defines a diffuserentry passage 26 from the radial outlet 20 of the pump 10 to a toroidalshaped collector 27. The impeller wheel 14 extends from a rotatableshaft 28, coupled for rotation in bearings (not shown). As will becomeapparent from the following description, the present invention may beapplied to many types of centrifugal pumps and the structure shown inFIG. 1 is merely meant to be illustrative, and not limiting in anymanner.

Referring now to FIG. 2, a portion of the centrifugal pump 10 of FIG. 1is illustrated, showing one form of applicant's invention. Moreparticularly, the centrifugal pump 10 of FIG. 2 includes a conventionalshrouded impeller 14 having a plurality of impeller blades 16. Forexample, fifteen such impeller blades 16 are shown. Each of the blades16 is disposed such that rotational velocity is imparted to the fluid(fuel flow) as it flows radially outward through the passage 19 formedby each set of adjacent blades 16.

Circumferentially surrounding the impeller 14 is the stationary diffuser22, now including certain features of the present invention. Thestationary diffuser 22 is separated by a predetermined radial distanced, typically from about 0.010 to about 0.100 inches, from the rotatingblade tips 16A of the impeller 14. The diffuser 22 includes a pluralityof diffuser entry passages 26. More particularly, in FIG. 2, four suchdiffuser passageways 26 are shown, substantially equally spacedcircumferentially about the diffuser 22. In one such embodiment, wherethe impeller 14 has a diameter of 3.8 inches, the diffuser inner surface22S is spaced a distance d of 0.019 inches from the blade tips 16A. Thediffuser passageways 26 provide an increase in flow area outwardly so asto deaccelerate the fuel and convert kinetic energy therefrom intostatic pressure. Each of the diffuser passageways 26 includes an outersurface 26S which is preferably disposed generally tangentially to thecircumferential inner surface 22S of the diffuser 22.

The vaned diffuser 22 also includes a plurality of recirculation means40. More particularly, the diffuser 22 is provided on itscircumferential inner surface 22S with a plurality of recirculationchannels 40. For example, eight such recirculation channels 40 are shownin FIG. 2. The recirculation channels 40 are substantially equallyspaced circumferentially in four pairs of two channels 40 along theinner surface 22S of the diffuser 22. In the form of the invention shownin FIG. 1, two of such channels 40 are disposed between each consecutivepair of diffuser passageways 26. Each such channel 40, and diffuserpassageway 26, preferably extend axially to substantially the samedistance as the axial width of the impeller tip 16A shown in FIG. 1. Therecirculation channels 40 include an outer wall 40S which is preferablydisposed generally tangentially to the inner surface 22S of the diffuser22. The recirculation channels 40 further include a redirecting wall 40Rwhich is preferably disposed generally radially with respect to thecenter of the impeller 14.

Referring now to FIG. 3, the purpose and function of the form ofinvention shown in FIG. 2 will be further discussed. For purpose ofsimplicity, the diagrammatic representation of the invention shown inFIG. 3 includes a limited number of impeller blades 16. Arrow R isintended to depict the direction of rotation of the impeller 14. Arrow Orepresents the fuel flow output from the diffuser 22. Arrow C isintended to depict an exemplary recirculation fuel flow between therecirculation channels 40 and impeller blade passageways 19.

More particularly, fuel flow enters at the center of the impeller 14and, through rotation of the impeller 14, discharges through thediffuser passageways 26 (arrow O). To promote the degradation of theantimisting fuel, it is desirable to shear the antimisting fuel in thedegradation region X defined by the relatively close clearance space, d,between the impeller blade tips 16A and the diffuser innercircumferential surface 22S. The impeller tip speed is typicallyrelatively high, e.g., between about 250 to about 450 feet per second,preferably at least about 300 feet per second. In this speed range, themolecular forces or stresses are caused to be of sufficient magnitude tocause molecular fragmentation of the antimisting fuel polymer additive,and hence, degradation of the antimisting fuel.

In addition to the stress provided in a single pass of fuel flow throughthe degradation region disposed between the impeller blade tips 16A andthe diffuser 22 and then radially out of the pump, the form ofinvention, shown in FIGS. 2 and 3, also promotes a high degree of mixingbetween the degraded and undegraded entering fuel entering the pump.Further, the invention provides for a high number of repetitive shearingevents. In this connection, between shearing locations in thedegradation region X, the recirculation channels 40 are provided topromote continuity of the recirculation flow and to encourage repetitiveshearing events. For example, as shown by the arrows C at therecirculation channels 40, additional shearing events are provided aseach of the blade tips 16A shear through the recirculation flow C (seearrows) produced by the recirculation channels 40.

It is important to recognize that the configuration of the recirculationchannels 40 are typically selected in accordance with the applicationinvolved. It is to be further recognized that the present inventionprovides means for degrading the antimisting fuel in a centrifugal pumpwhile at the same time providing useful fuel flow and pressure, withoutrequiring excessive energy input or creating unacceptable fueltemperature rise.

EXAMPLES

The invention may be better appreciated by reference now to thefollowing examples. However, it is to be understood that the inventionis not limited to the details recited therein.

EXAMPLE #1

In the development of the present invention, a conventional centrifugalfuel pump suitable for aircraft application, substantially the same asthe one shown in FIG. 1 (not including recirculation channels) wastested with antimisting fuel. The antimisting fuel comprised JET-A fuel(aircraft grade kerosene) and about 0.3% by weight of Imperial ChemicalIndustries (ICI) fuel modifier FM-9.

The fuel flow input to the pump was 5991 pounds per hour at cruise rpmand 15759 pounds per hour at takeoff rpm. The pump was rotated at 24558rpm at cruise and 26015 rpm at takeoff. The pump shaft power was 77horsepower at cruise rpm and 113 horsepower at takeoff rpm. The pumpinput to pump output temperature rise was 56° F. at cruise rpm and 26°F. at takeoff rpm. The pressure output of the pump was 1001 psig atcruise rpm and 1121 psig at takeoff rpm.

The antimisting fuel degrading capability of the pump was determinedusing a standardized method based on the ratio of (1) the time forantimisting fuel to pass through a 17 micron screen divided by (2) thecorresponding time for the reference JET-A fuel: ##EQU1##

A curve showing the fuel degradation characteristics of the pump isshown in dashed line in FIG. 4. As shown, the curve passes through thetakeoff and cruise power points with Filter Ratios of 8.2 and 1.8,respectively. It is to be appreciated that completely degradedantimisting fuel would exhibit a horizontal line with a Filter Ratiovalue of 1, as shown in dashed line, while presently desired antimistingfuel Filter Ratios for aircraft gas turbine engines are not greater thanabout 2.5 at takeoff and about 1.2 at cruise.

EXAMPLE #2

The pump of EXAMPLE #1 was modified to include the diffuser 22 of FIG.2, and its associated recirculation channels 40.

This pump was tested under conditions similar to EXAMPLE 190 1. Moreparticularly, the fuel flow to the pump was 5693 pounds per hour atcruise rpm and 15244 pounds per hour at takeoff rpm. The pump wasrotated at 24552 rpm at cruise and 25988 rpm at takeoff. The pump shaftpower was 89 horsepower at cruise rpm and 128 horsepower at takeoff rpm.The pump input to pump output temperature rise was 70° C. at cruise rpmand 33° F. at takeoff rpm. The pressure output of this pump was 980 psigat cruise rpm and 1090 psig at takeoff rpm.

A curve showing the improved degradation characteristics of this pump isshown in dashed line in FIG. 5. The curve of FIG. 5 passes through thetakeoff and cruise power points with Filter Ratios of 2.3 and 1.2,respectively.

It is to be appreciated that the degradation characteristics shown inFIG. 6 approach the completely degraded fuel characteristic in thecruise power region, the dominant operating region of an aircraft gasturbine engine.

General Considerations

As discussed earlier, the particular configuration of the antimistingcentrifugal fuel pump of the present invention is typically selected fora given application. However, the following guidelines should beconsidered in selecting a particular configuration. Where increasedinternal fuel flow recirculation is desired for increased shearingactivity, relatively wider impeller blades should be provided as therecirculating flow is increased by the use of wider impeller blades.Further, the provision of higher impeller tip blade angles (more radialat the impeller discharge) tends to increase blade loading, one of thefactors promoting the fuel flow recirculation. Also, relatively fewerimpeller blades result in higher individual blade loading.

Another form of the invention is partially shown in FIG. 6 wherein,where possible, prime reference numerals (') have been employed torepresent corresponding elements to the form of invention shown in FIGS.2 and 3. As shown in FIG. 6, axially positioned recirculation channels40' may be provided at the discharge of the impeller 14'. To provide forthe resulting axial recirculation flow (C'), the impeller forward shroud17' is shown radially shortened. It is to be recognized that the axialrecirculation channel 40' can replace or augment the radialrecirculation channels 40 of FIGS. 2 and 3. The axial recirculationchannels 40' provide more recirculation because the fuel moves between arelatively high (H) and low (L) static pressure region of the diffuser22' and impeller 14', respectively. Of course, the axial recirculationchannels 40' may require more power input to the pump for the same levelof degradation afforded by the form of the invention shown in FIG. 3.

In view of the foregoing, the optimum design solution for a givenapplication will be the one which yields a maximum amount ofrecirculation between the impeller discharge and the discharge casingwith power losses being confined to promotion of localized recirculationflow near the impeller tip where adequate impeller blade tip velocity isavailable to produce the molecular forces or stresses needed to degradethe antimisting fuel.

Thus, there is provided by the present invention a centrifugal pumpproviding an acceptable level of degradation to permit satisfactoryengine operation at substantially all conditions. In addition, theantimisting centrifugal fuel pump of the present invention is capable ofpumping the fuel at the ordinarily desired speed, e.g., about 25000 rpm,and flow levels while simultaneously providing antimisting fueldegrading capability and desired pressure levels. Further, acceptableincreases in extracted engine power and fuel temperature rise isprovided in the antimisting centrifugal fuel pump of the presentinvention. Also, no additional compromises to the safety, reliability orcost aspects are encountered in operating the aircraft or engine withthe antimisting centrifugal pump of the present invention.

In the present invention, apparatus and methods are provided fordegrading antimisting fuel. In particular, antimisting fuel is guidedinto a rotating impeller and by means of change of fluid angularmomentum, raised to a higher level of static and dynamic pressure at theimpeller discharge tip. Then, by means of interaction between theimpeller and a stationary device surrounding the impeller, molecularforces or stresses cause degradation of the antimisting fuel. Further, asecondary flow field or recirculation between the impeller andsurrounding stationary device promotes additional degradation as aresult of repetition of the degradation mechanisms.

The antimisting fuel pump of the present invention may, for example, bemounted to the engine or located between the aircraft fuel and theengine fuel inlet. The means for driving the antimisting fuel pump may,for example, comprise the engine shaft, gearbox power, an electricmotor, a pneumatic drive, or hydraulic drive.

Further, although the method and apparatus of the present invention havebeen described in connection with a conventional centrifugal pump havinga shrouded impeller, the invention is generally applicable to otherforms of centrifugal pumps. In addition, the size and configuration ofthe centrifugal pumps of the present invention, as hereinbeforedescribed, are exemplary and not intended to be limiting in any manner.For example, an important advantage of the method and apparatus of thepresent invention is that the invention can be practiced through simplemodification to conventional centrifugal pumps. In this connection, formany applications, it is preferable to employ the existing conventionalcentrifugal pump and make the simplest modification thereto so as toprovide the degradation region which is required for the involvedapplication and antimisting fuel.

While the present invention has been described with reference tospecific embodiments thereof, it will be obvious to those skilled in theart that various changes and modifications may be made without departingfrom the invention in its broader aspects. It is contemplated in theappended claims to cover all such variations and modifications whichcome within the true spirit and scope of my invention.

What I claim as new and desire to be secured by Letters Patent of theUnited States Patent and Trademark Office is:
 1. Apparatus for degradingantimisting fuel, the apparatus including a centrifugal pump having arotary impeller with a substantially centrally located input forreceiving fuel and being closely surrounded by a vaned collector forreceiving fuel from an output of the rotary impeller, the rotaryimpeller including a plurality of radial impeller blades, whichcomprises:recirculation means for repetitively directing some of thefuel which passes from said rotary impeller to said vaned collector backto said impeller for enhancing the degradation of said fuel. 2.Apparatus in accordance with claim 1 in which said recirculation meanscomprises a plurality of recirculation channels in said vaned collector.3. Apparatus in accordance with claim 2 in which said vaned collectorcomprises a diffuser having a plurality of diffuser passageways. 4.Apparatus in accordance with claim 3 in which said diffuser includes agenerally circumferential inner surface spaced a predetermined distancefrom said rotary impeller blades and said recirculation channels aredisposed along said inner surface, said recirculation channels beinggenerally radially aligned with said rotary impeller.
 5. Apparatus inaccordance with claim 4 in which said recirculation channels include anouter wall disposed generally tangentially to said inner surface of saiddiffuser and a redirecting wall disposed generally radially with respectto said rotary impeller.
 6. Apparatus in accordance with claim 5 inwhich said diffuser passageways are substantially equally spacedcircumferentially along said inner surface of said diffuser. 7.Apparatus in accordance with claim 6 in which at least one of saidrecirculation channels is disposed between each consecutive pair of saiddiffuser passageways.
 8. Apparatus in accordance with claim 7 in whichat least one pair of said recirculation channels is disposed betweeneach consecutive pair of said diffuser passageways.
 9. Apparatus inaccordance with claim 8 in which said diffuser includes four diffuserpassageways and eight recirculation channels, said recirculationchannels being substantially equally spaced circumferentially in fourpairs of said channels, each of said pairs of channels being disposedbetween each consecutive pair of diffuser passageways.
 10. In acentrifugal pump having an impeller which bears blades and which rotateswithin a casing, there being a clearance between the blades and thecasing, the improvement comprising:(a) recirculation means in the casingwhich cause the clearance between a selected blade and the casing tochange during rotation, the change having no substantial function otherthan to recirculate fluid between the recirculation means and the blade,thereby subjecting the fluid to repeated shearing events.
 11. In acentrifugal pump in which an impeller receives fluid from an inlet anddrives the fluid radially outward toward two or more diffusers whichreceive the fluid and conduct the fluid to one or more outlets, theimprovement comprising:(a) a plurality of recirculators which areunconnected with the outlets and which receive outwardly travellingfluid and return received fluid toward the impeller.
 12. A degrader forfuel which contains an anti-misting component, comprising:(a) acentrifugal pump which contains(i) an inlet; (ii) an impeller forreceiving fuel from the inlet and which drives fuel in a radiallyoutward direction; (iii) a casing around and spaced from the impellerwhich contains openings for receiving fuel and for conducting fueltoward an outlet; and (iv) a plurality of recirculation means in thecasing which are unconnected with any outlet and which provides improvedfuel recirculation over the recirculation inherently present in thespace between the impeller and the casing.